This disclosure relates to surgical instruments, and in particular to surgical cutting instruments having two electrodes for providing coagulation and/or vaporization of tissue.
Surgical apparatus used to shave, cut, resect, abrade and/or remove tissue, bone and/or other bodily materials are known. Such surgical apparatus can include a cutting surface, such as a rotating blade disposed on an elongated inner tube that is rotated within an elongated outer tube having a cutting window. The inner and outer tubes together form a surgical cutting instrument or unit. In general, the elongated outer tube includes a distal end defining an opening or cutting window disposed at a side of the distal end of the outer tube. The cutting window of the outer tube exposes the cutting surface of the inner tube (typically located at a side of the distal end of the inner tube) to tissue, bone and/or any other bodily materials to be removed. A powered handpiece is used to rotate the inner tube with respect to the outer tube while an outer tube hub (connected to the proximal end of the outer tube) is fixed to the handpiece and an inner tube hub (connected to the proximal end of the inner tube) is loosely held by the powered handpiece and is rotated by a motor of the handpiece.
In some instruments, the inner tube is hollow and has a cutting window on a side surface of its distal end such that tissue, bone, etc., will be cut or shaved as the cutting window of the inner tube aligns with and then becomes misaligned with the cutting window of the outer tube as the inner tube is rotated within the outer tube. In this regard, it can be said that the cutting device nibbles or takes away small pieces of the bone, tissue, etc., as the inner tube is rotated within the outer tube.
In some instruments, a vacuum is applied through the inner tube such that the bodily material that is to be cut, shaved, etc., is drawn into the windows of the inner and outer tubes when those windows become aligned, thereby facilitating the cutting, shaving, etc., of the tissue, which then travels through the inner tube due to the suction. It also is common to supply an irrigation fluid, which can include a liquid, to the surgical site via a passage provided between the inner and outer tubes.
Microdebrider shaver blades are common instruments used in endoscopic surgery. The shaver blade delivers high speed mechanical cutting of tissue at a specified area of anatomy that the surgeon can reach through a minimally invasive incision or natural orifice. One challenge during procedures using such instruments can be the slowing down or stopping of bleeding (hemostasis) during the procedure. One solution for maintaining proper hemostasis during a procedure is to utilize an electrocautery instrument that can be used inside the same minimally invasive surgical corridor. In a minimally invasive procedure, every time the surgeon exchanges the cutting instrument for the electrocautery instrument there is a corresponding increase in the time required to perform the procedure and there is a risk of traumatizing the anatomy due to the exchange of the instruments. Thus, it is convenient to combine the mechanical cutting and electrocautery instruments to form one instrument performing both functions. By providing a microdebrider shaver blade that also can perform electrocautery, the need to perform tool exchanges at the surgical site is reduced and can even be eliminated.
There are two standard types of electrocautery: bipolar and monopolar. Monopolar cautery uses one electrode at the surgical site and then relies on a neutral electrode placed somewhere else on the patient (typically on the skin of the patient) to help disperse the energy enough to pass the energy safely through the patient. Bipolar cautery does not use a separate neutral electrode. Instead, bipolar cautery delivers the energy and returns the energy through the device using two electrodes at the surgical site. That is, a bipolar device will provide two electrodes at the surgical site, one active electrode and one return electrode.
For typical sinus surgery, the bipolar electrode is preferred due to the close proximity of critical anatomy to the typical surgery sites in the sinuses. That is, a bipolar device enables the energy to be applied at a more focused location.
It is known to provide microdebrider shaver blades with bipolar energy electrodes. The bipolar shaver blades utilize a series of overlapping layers to provide the two electrodes needed to transfer energy into the tissue at the surgical site to achieve coagulation. In the known structure, two concentric electrically conductive layers are electrically isolated from each other in order to establish the two isolated electrodes used for bipolar cautery. An example of such a known structure is shown in FIG. 1. The FIG. 1 microdebrider includes a stationary outer tubular member 110 and a rotatable inner tubular member 130 that rotates within the outer tubular member 110. The outer tubular member 110 includes a sideward-facing opening at its distal end which has multiple cutting teeth 112 so as to form a cutting window at the distal end of the outer tubular member 110. The inner, rotatable tubular member (cutting member) 130 also includes a sideward-facing opening having multiple cutting teeth 132. As is known, cutting or shaving takes place by rotating the inner tubular member 130 within the outer tubular member 110 while applying suction through the tubular member 130. In addition, irrigation fluid can be provided to the surgical site through a gap that is formed between the outer tubular member 110 and the inner tubular member 130. In the FIG. 1 cauterizing microdebrider, the outer tubular member 110 is electrically conductive and forms one of the two electrodes of the bipolar electrocautery instrument. An electrically insulative film 115 covers most of the outer surface of the stationary, outer tubular member 110 so that only the teeth 112 and a narrow strip at the distal-most tip of the outer tubular member 110 are not covered by the insulating film 115. The narrow strip at the distal-most tip defines one of the electrodes (for example, the active electrode). An electrically conductive layer or film 120 is formed over part of the insulating film 115. The electrically conductive layer 120 (also called a sheath) forms the second electrode (for example, the return electrode) of the bipolar electrocautery instrument. An outermost electrically insulating layer or film 140 is then formed over most of the instrument except for the distal end thereof so that the electrically conductive layer 120 is exposed only at the distal end of the instrument.
The known design shown in FIG. 1 results in a horseshoe-shaped area of the electrically insulating film 115 being present between the two electrodes formed by the tip of the outer tubular member 110 and the distal end of the electrically conductive layer 120. This design restricts (limits) the separation distance that is possible between the two electrodes (the electrode formed at the tip of member 110 and the electrode formed by layer 120) in that it becomes more difficult to obtain good contact between the tissue and each electrode as one increases the separation between the two different layers which form the two electrodes. In other words, because the electrode formed by the tip of tubular member 110 is recessed compared to the electrode formed by layer 120, it can be difficult to cause both electrodes to contact the tissue that is to be cauterized. In addition, because the electrode formed by layer 120 surrounds the electrode formed at the tip of member 110, it can be difficult to place the electrodes (one of which is an active electrode and the other of which is a return electrode) on opposite sides of the tissue that is to be cauterized.